Research

A two-phase closed thermosyphon is a wickless and passive heat transfer device. In the thermosyphon, working fluid vaporizes in the lower evaporator section, and then the vapor condenses in the upper condenser section and returns to the evaporator section by gravitational force. Thermosyphons can be widely used for industrial applications, including heat exchangers, solar collectors, and cooling of electrical devices, batteries, and avionics equipment. These applications, however, may be encountered in diverse dynamic circumstances such as acceleration, rotation, and vibration.  As a first step to make a thermosyphon function properly and improve its heat transfer performance under dynamic conditions, we experimentally investigate boiling patterns of the thermosyphon, when it is subjected to horizontal vibration, by varying the amplitude and frequency of vibration, heat input, and filling ratio. A new parameter which characterizes the intensity of vibration is introduced to determine the effect of horizontal vibration on phase change inside the thermosyphon. When the thermosyphon is subjected to the case of a large vibration-intensity parameter, boiling is suppressed due to the high requirement of superheat. Furthermore, as heat input into the thermosyphon increases, the effects of severe horizontal vibration on boiling suppression are annihilated.

A fluidic oscillator, which generates unsteady sweeping jet without any actuator and moving parts, has received much attention due to its attractive features: high durability to shock and vibration and no electromagnetic interference. We apply the fluidic oscillator to improve the performance of convective heat transfer. The sweeping jet impinges vertically on a heated flat plate. By varying Reynolds number and nozzle-to-plate spacing, we experimentally investigate the characteristics of a heat transfer rate of the plate and examine flow fields to find the flow characteristics responsible for enhancing heat transfer.